Dyed polyvinyl carbazole photoconductive layer

ABSTRACT

A photosensitive layer for use in electrophotography having increased sensitivity to light in the visible spectrum is obtained by incorporating certain carbazolyl radical-containing dyes into a polyvinyl carbazole photoconductive layer.

United States Patent [1 1 [i 3,923,508

Kriz et al. i 1 Dec. 2, 1975 1 DYED POLYVINYL CARBAZOLE 3,647,433 3/1972 Contois 96/].5

PHOTOCONDUCTIVE LAYER [75] lnventors: Karel Kriz, Marlboro, Mass; Susan Primary Examiner chafles L Bowers, Jr-

B. German, Barrmgton; John J. Krajewski wheeling both of m Assistant ExammerJ0hn L. Goodrow Attorney, Agent, or Firm-Dressler, Goldsmith, [73] Assignee: DeSoto, Inc., Des Plaines, Ill, Clement & Gordon, Ltd.

[22] Filed: Jan. 10, 1974 [21] AppL N0.: 432,254

[57] ABSTRACT [52] US. Cl. 96/1.6 [51] Int. Cl. 6036 5/09 A ph tosensitive l yer for use in electrophotography [58] Field of Search 96/15, 1.6, 1 R, 1.7; having increased sensitivity to light in the visible spec- 260/240 A trum is obtained by incorporating certain carbazolyl radical-containing dyes into a polyvinyl carbazole pho- [56] References Cited toconductive layer.

UNITED STATES PATENTS 3,579,331 5/1971 Mee 96/l.5 8 Claims, No Drawings DYED POLYVINYL CARBAZOLE PHOTOCONDUCTIVE LAYER The present invention relates to the provision of a photoconductive layer based on polyvinyl carbazole having superior properties for use in electrophotography. More particularly, this invention relates to the incorporation of a carbazole radical-containing dye into the photoconductive layer in order to increase the photosensitivity of the layer to visible light with a minimum of background coloration.

in electrophotography, it is desirable to have a photoconductive layer which is highly sensitive to light in the visible spectrum, as well as being capable of maintaining a high level of charge. The use of polyvinyl carbazole to provide the photoconductive layer and addition of dyes thereto in order to obtain the desired light sensitivity and increased speed is well known. Additionally, dyes which impart a minimum of color to the photoconductive layer are desirable for optimum contrast.

It has now been found that certain carbazolyl radicalcontaining dyes, when incorporated into a polyvinyl carbazole photoconductive layer, increase the layers sensitivity to light while minimizing the coloration of the layer, thus minimizing loss of contrast, while extending the sensitivity to the visible region of the spectrum and maximizing the photoconductive speed.

Referring more particularly to the carbazolyl radicalcontaining dyes which are used in this invention, these are described by the following structure:

in which R is hydrogen or an alkyl group having from 1 to 10 carbon atoms, preferably from 2 to 4 carbon atoms, and X identifies a negative counterion which may be monovalent or polyvalent, but preferably monovalent.

It will be seen that the carbazole radical-containing dyes are quaternary nitrogen compounds which are believed to exist in ionic form as shown in the formula. Any suitable negative ion, such as Cl, Br, N0 S0 P0 and 010,- can be employed, though the Clion is particularly preferred and its use will be illustrated herein. Also, best results are obtained when R has 4 carbon atoms or less.

The polyvinyl carbazole used in the present invention is a well known polymer, the formation of which is disclosed in various ways in the literature of the art, as for example as shown in US. Pat. Nos. 3,503,740 and 3,037,861. Polyvinyl carbazole is also available in commerce.

A preferred polyvinyl carbazole is produced as follows, this being the subject of application Ser. No. 285,374, filed Aug. 22, 1972.

EXAMPLE 1 spread to a depth of about inch onto a stainless steel conveyor belt moving at about 6.8 ft./min. The material was conveyed under a bank of three 6000 watt IR heaters (20.4 seconds of heat) where it melted and polymerized; then under an exhaust hood, and finally over a cold water bath. The resulting polymer was broken and pulverized to a usable bead form. A- 20% solution in toluene had a Gardner viscosity of Y.

It is preferred in this invention to dissolve the polyvinyl carbazole in a solvent, such as toluene, chlorobenzene, or tetrahydrofuran, in a concentration of from 4% to 15%, a concentration of about 5% to 10% being particularly preferred. The carbazolyl radical-containing dye is then added in a proportion of from about l X 10 mole of dye per gram of polyvinyl carbazole to about 1 X 10' mole of dye per gram of polyvinyl carbazole.

It is preferred to use as little dye as is consistent with approximate maximization of photoconductive response, so about 1 X 10 mole of dye per gram of polyvinyl carbazole is preferred. There is little advantage to the use of a greater concentration of dye since the increase in light sensitivity is small while the extra dye may lower charge acceptance as well as producing a darker color which decreases print contrast. The solution of polyvinyl carbazole and dye is then coated either onto a conductive base, and dried to form a coating, or the solution can be coated onto a nonadherent surface, dried and the resulting film is stripped for use as desired.

It is possible to add plasticizers, other resins, or additives to the solution as known to theart to modify the characteristics of the final film, but these are not necessary. Dicyclohexyl phthalate and chlorinated paraffin are superior plasticizers since they do not detract from the photoconductive response.

It will be understood that the term layer is used with its generic connotation to include free films, coatings, and even impregnations. Of course, the substrate on which the layer is supported will normally be electrically conductive, such as a metal foil, and the coating may be strongly adherent, or easily strippable from the backing. Surface impregnations of conductive paper are also contemplated.

EXAMPLE 2 The polyvinyl carbazole of Example 1 was dissolved in chlorobenzene to provide a 10% solution and 0.2 gram of methanol was added per gram of polyvinyl carbazole to insure solubility of the dye iii the solution.

Plasticizers were added, namely, 0.2 gram of dicyclohexyl phthalate and 0.2 gram of chlorinated paraffin per gram of polyvinyl carbazole. The dye to be tested was then dissolved in the solution to provide various dye concentrations, and these solutions were coated on anodized aluminum strips using a wire wound rod to obtain coating weights in the range of 3-4 lbs/3000 ft The coated strips were charged in the dark using a negative corona and the charged strips were then exposed in contact with a sensitometric step wedge (K 015) by a tungsten light; 100 f.c., sec. The latent image (surface voltages of each step) was measured by Monroe electrostatic probe 1009B and the latter plotted vs. log of the exposure. The speed indicator was extrapolated from the curve as the exposure (foot candle seconds) required for total discharge.

Two different dyes were used. First, Crystal Violet was used since it well illustrates conventional practice. Second the dye di(4-dimethylaminophenyl)-3-carbazyl carbonium chloride wasused as illustrative of this invention, with its production being given hereinafter.

plete discharge. Moreover, there is much less discoloration, the film absorption being only 0.01 which is.

roughly 98% light transmission. Note 1 Light absorption is measured on Mylar film at 510 nanometers.

EXAMPLE 3 Production of di-(4-dimethylaminophenyl)-3'-carbazy l carbonium chloride.

Michlers ketone (13.4 grams, 0.05 mole) and carbazole (8.7 grams, 0.05 mole) were stirred with 50 ml. of chlorobenzene in an Erlenmeyer flask. Phosphorus ox? ychloride (7.7 grams, 0.05 mole) was added and the flask closed lightly with a wad of glass wool. The mixture was stirred and heated 16 hours near reflux. The resulting deep blue mass was allowed to cool and then stirred with I00 ml. of water and filtered. The filtrate was extracted with two 75 ml. portion of dichloromethane and the organic layer dried and concentrated to yield 15 grams (70% yield) of deep blue dye.

The invention is defined in the claims which follow.

Dye Concentration Speed Film Absorption Mole Dye per Gram Foot Candle at 510 nm Polyvinylcarbazole Seconds (see Note 1) Crystal Crystal Crystal Violet Example 3 Violet Example 3 Violet Example 3 l X 10" 2000 0.00 2.5 X 10" 1700 0.00 5 X 10 l200 0.0l

- l X 10 600 2300 0.01 0.00 l X IO 2.5 X 10 2.5 X 10" 450 i000 0.04 0.00 5 X 10' 5 X 10" 350 550 0.09 0.00 l X 10" l X 10 400 200 0.01 2.5 X [0' 200 0.03 5 X 10 200 0.05 l X 10 300 0.13

The above comparison shows that, using Crystal Violet, the maximum photoconductive speed was 350 foot candle seconds for complete discharge and the film absorption was 0.09 indicating roughly 90% light transmission. These values are obtained at a dye concentra tion of 5 X 10". When the dye of this invention is used, somewhat more dye is required for maximum speed, namely 1 X 10", but the system is considerably faster, only 200 foot candle seconds being needed for com- We claim: 1. A photoconductive layer sensitive to visible light comprising polyvinyl carbazole and a dye having the structure:

where R is hydrogen or an alkyl group having from 1 to 10 carbon atoms, and X is a negative counterion, said dye being present in said polyvinyl carbazole in a proportion of from about 1 X 10- to about 1 X 10" mole of dye per gram of polyvinyl carbazole.

2. A photoconductive layer as recited in claim 1 in 6. A solution adapted to deposit a photoconductive which said photoconductive layer consists essentially of layer comprising an organic solvent having dissolved said polyvinyl carbazole and said dye and R is an alkyl therein polyvinyl carbazole and from l X to about group having from 2 to 4 carbon atoms. 1 X 10 mole of dye per gram of polyvinyl carbazole,

3. A photoconductive layer as recited in claim 1 in 5 said dye having the structure:

which X is Cl. where R is hydrogen or an alkyl group having from 1 to 4. A photoconductive layer as recited in claim 3 in 10 carbon atoms, and X is a negative counterion. which R contains less than 4 carbon atoms. 7. A solution as recited in claim 6 further comprising 5. A photoconductive layer as recited in claim 4 in dicyclohexyl phthalate. which said dye is present in a proportion of about 1 X 8. A solution as recited in claim 6 further comprising 10 mole of dye per gram of polyvinyl carbazole. chlorinated paraffin.

UNITED STATES PATENT OFFICE CERTIFIQATE @F CORRECTION 5 PATENTNO. 3,923,508

DATED I December 2, 1975 |NVENTOR(S): Karel.Kriz, Susan B. Gorman, and

John J. Kraj ewski I I It rs certrtred that error appears rh the ab0ve-identrfred patent and that sard Letters Patent Q are hereby corrected as shown below:

Column 4, claim 1, line 4, the formula should read:

Signed and Sealed this D t e [SEAL] w ntzeth Day Of Aprzl1976 Arrest: I

C. MARSHALL DANN g jjrcer (mnmr'ssr'mrvr oj'larenrs and Trademarks 

2. A photoconductive layer as recited in claim 1 in which said photoconductive layer consists essentially of said polyvinyl carbazole and said dye and R is an alkyl group having from 2 to 4 carbon atoms.
 3. A photoconductive layer as recited in claim 1 in which X is Cl .
 4. A photoconductive layer as recited in claim 3 in which R contains less than 4 carbon atoms.
 5. A photoconductive layer as recited in claim 4 in which said dye is present in a proportion of about 1 X 10 5 mole of dye per gram of polyvinyl carbazole.
 6. A solution adapted to deposit a photoconductive layer comprising an organic solvent having dissolved therein polyvinyl carbazole and from 1 X 10 6 to about 1 X 10 4 mole of dye per gram of polyvinyl carbazole, said dye having the structure:
 7. A solution as recited in claim 6 further comprising dicyclohexyl phthalate.
 8. A solution as recited in claim 6 further comprising chlorinated paraffin. 